The falling film evaporator is a kind of high efficiency evaporation equipment, which is called the film evaporator with the rising film evaporator and the scraper type thin film evaporator. Thin film evaporator has obvious advantages and is widely used in chemical industry, light industry and food processing industry to achieve the purpose of liquid concentration. The structure of falling film evaporator is not complicated, can be understood as a simple vertical tube for a cloth membrane device heater, heat exchanger and ordinary but it has an obvious difference, the shell is fixed to the heating fluid, Guan Cheng fixed evaporated material.
Falling film evaporator tube take materials are from the top of pipe in the heat exchanger tube, with its own gravity to the downstream along the tube wall in the heat exchanger tube before, after the cloth membrane cloth membrane, which enters the heat exchanger tube is thin, in the process of material from the top to the bottom water is evaporated sent out, so as to achieve the purpose of material concentration, the shell if it is heated by condensing steam heating or heat conducting oil, if the use of steam coming out under, if the selection of heat conducting oil should be bottom-up. Thus it can be seen that the flow direction of the medium and outside the tube is not always countercurrent.
But this is not important, because the pressure inside the tube is basically unchanged, which will not cause the change of the fluid temperature。 The change of medium temperature in the tube is due to the increase of boiling point due to the change of medium concentration, which is only a slight increase。
Analysis of the advantages of the falling film evaporator:
(1) change of the material in the heat pipe with short residence time, does not affect the chemical properties of heat sensitive materials;
(2) the material in the heat exchange tube is thin film and the flow velocity is fast, and the heat transfer coefficient is large.
(3) the pressure drop is almost 0, and the pipe material is in the atmospheric pressure environment. It can flow down along the inner wall of the pipe entirely, and it can save energy. (4) because the pipe material flows downward along the inner wall of the pipe itself instead of the pressure difference, the low temperature difference can be chosen.
(5) there is very little retention of space materials in the tube range;
(6) the tube material is heated by convection boiling, so the surface state of the heat transfer tube almost does not affect the boiling of the material. Shortcoming analysis of falling film evaporator:
(1) the effect of the evaporation of the equipment is directly related to the distributor, and the requirements for the design, manufacture and installation of the distributor are very high。
(2) the equipment installation requirements, mainly for the requirement of verticality, assuming the tube length is 9m, is less than 6. 4mm vertical equipment;
(3) it is necessary to ensure that the inner wall of the heat exchanger tube is completely wet, but the thickness of the film can not be too large. It is necessary to design and calculate the material feed quantity and the length of the heat exchanger tube accurately.
(4 because of the high requirements of design and manufacture, the cost of equipment procurement is very high;
(5) it is not applicable to materials that are easily fouled or containing solid suspension.